An audio microphone is commonly used in various consumer applications such as cellular phones, digital audio recorders, personal computers, and teleconferencing systems. Particularly, a low cost electret condenser microphone (ECM) is used in mass-produced cost-sensitive applications. The ECM microphone typically includes a film made of an electret material and mounted in a small package having a sound port and an electrical output terminal. The electret material is attached to a diaphragm or constitutes the diaphragm itself. As another type of microphone, there is a micro electro-mechanical system (MEMS) microphone and in this MEMS microphone, a pressure-sensitive diaphragm may be implemented on an integrated circuit.
Among them, the audio microphone used in communication devices requires immunity to radio frequency (RF) signals. A voice frequency band of the microphone is used in about 40 kHz or less, but a frequency band used for communication ranges from several hundreds of MHz to several GHz.
Such a high frequency communication carrier may be demodulated into a voice band by internal or external mechanisms or elements of the microphone. Therefore, the communication frequency has an influence on a voice frequency, so that the performance of the microphone is deteriorated.
Particularly, in the case of communication devices using a time division multiple access (TDMA) scheme, since a power amplifier periodically operates in accordance with a periodic transmission (Tx) operation of the communication devices, there is a problem that TDMA noise has an influence on the microphone. Accordingly, a microphone system insensitive to such external noise is required.
In general, in order to prevent external noise from being introduced into a microphone system, a low pass filter may be provided at the power supply VDD and output OUT of a microphone module. However, since such a filter is exposed to the outside of the microphone module and a capacitor for filtering is added to the outside of the microphone module, there is a problem that cost increases and productivity is reduced.
Furthermore, since the external noise may also be introduced through pads connected between a microphone sensor and an integrated circuit as well as the power supply VDD and output OUT of the microphone module, the noise introduced through such pads may not be filtered by a filter connected to the power supply VDD and output of the microphone module.